This invention relates to an optical cross-connector, and more specifically to an optical cross-connector of a redundant configuration to control paths of optical signals.
Keeping pace with the spread of the Internet, a big demand for a larger transmission capacity has skyrocketed. An optical a fiber transmission system is suitable for a large capacity data transmission. In particular, high-speed data transmission is easily realized by using a wavelength multiplexing transmission system to transmit a plurality of optical signals having different wavelengths. The number of multiplexed wavelengths per fiber and the transmission capacity to be required per user has strikingly increased. In recent years, such a system to offer one wavelength for one user as an exclusive channel has been strongly demanded. A conventional configuration in which an electric network switching apparatus is disposed per wavelength to demultiplex into low-speed electric interfaces, add/drop, and cross-connect at a low-speed interface unit has severe problems of increasing the cost, reducing the operational efficiency, and extending the installation space of terminal stations. Accordingly, a realization of an optical network switching apparatus having effective functions of path housing, adding/dropping, and network switching has expected.
In an optical network switching apparatus, a changeover switch is necessary to realize adding/dropping of wavelength channels and switching of paths. As the changeover-switching element, an optical matrix switch to connect between desired input and output fibers by selectively standing each mirror disposed on each node of matrixes has attracted a great deal of attention (see U.S. Pat. No. 5,960,132). This optical matrix switch has a merit to be fabricated compact using micro-machining technology.
To realize a continuous operation even if a matrix switch has a failure, it is necessary to make matrix switches redundant. For instance, in a dual configuration in which two matrix switches are prepared, one is for working and the other is for protection, it is required to dispose optical splitters of the same number with the input fibers on the input side to distribute input optical signals to the same input ports of the two matrix switches, and also to dispose optical selectors of the same number with the output fibers on the output side to select one of the same output ports of the two matrix switches. In short, in this configuration, it is necessary to dispose optical selector switches of the same number with the output ports of the matrix switches.
However, in this configuration, a break of approximately 10 ms basically occurs when the optical selector switch switches over. This break causes an extremely large amount of loss in recent ultra-high speed transmission systems, and thus it is undesirable.
Furthermore, the optical selector switch is fundamentally an active component and not reliable. Therefore, the reliability of the whole apparatus, namely the reliability of the service traffic, is remarkably lowered as the number of the optical selector switches increases proportional to the number of the output fibers. This is because that the reliability of the whole apparatus is determined depending on the reliability of the optical selector switch (more specifically, it is calculated by raising the reliability of a signal optical selector switch to the power of the number of the optical selector switches) rather than the reliability of the matrix switches.
When any optical selector switch breaks, the broken one is naturally replaced. The replacement takes mean time to repair (MTTR) at least one hour and even one day in a prolonged case, and the main signal path is broken during the repair time. This means to stop the communication service, and this is a severe problem.
When all optical selectors are mounted on a single substrate, the whole substrate is replaced, and when each optical selector switch is mounted on a separate substrate, the broken optical selector switch alone is replaced. In the latter case, although there is a merit that signal paths having no connection with the broken selector switch can be maintained in the present state, there is also a demerit that the housing efficiency deteriorates as the number of the output fibers increases. For example, even in a common four-fiber ring network, it is necessary to dispose eight optical selector switch substrates because eight output optical fibers exist.
It is therefore an object of the present invention to provide an optical cross-connector to double matrix switches and realize higher reliability.
An optical cross-connector according to the invention consists of first and second optical distributors, each distributor having a plurality of input and output ports, a first connecting mode to connect between desired input and output ports, and second connecting mode to block outputting of input lights of all the input ports; a splitter to split each of a plurality of input optical signals into two portions and apply them to each input port of the first and second optical distributors; a combiner to combine output lights from mutually corresponding output ports of the first and second optical distributors; and a controller to switch between a first control state to set the first optical distributor in the first connecting mode and the second optical distributor in the second connecting mode and a second control state to set the first optical distributor in the second connecting mode and the second optical distributor in the first connecting mode.
The above configuration can make the optical distribution redundant using fewer movable components.
Preferably, the first optical distributor consists of a first optical switch having a plurality of input and output ports to connect between desired input and output ports in the first connecting mode and connect input lights of all the input ports to at least one predetermined output port in the second connecting mode and at least one first optical shutter disposed between the at least one predetermined output port of the first optical switch and a corresponding input port of the combiner to transmit light in the first connecting mode and block light in the second connecting mode, and the second optical distributor consists of a second optical switch having a plurality of input and output ports to connect between desired input and output ports in the first connecting mode and connect input lights of all the input ports to at least one predetermined output port in the second connecting mode and at least one second optical shutter disposed between the at least one predetermined output port of the second optical switch and a corresponding input port of the combiner to transmit light in the first connecting mode and block light in the second connecting mode.
According to this configuration, it is sufficient if at least one optical shutter is disposed on each optical switch. Even if the number of output lines is increased, two optical shutters at the minimum are sufficient for each optical switch. Therefore, the reliability improves remarkably.
Preferably, the optical cross-connector according to the invention further consists of a first input detector to detect input light of each input port of the first optical switch, a second input detector to detect input light of each input port of the second optical switch, a first output detector to detect output light from each output port of the first optical switch, a second output detector to detect output light from each output port of the second optical switch, and a supervisor to monitor the detection outputs from the first and second input detectors and first and second output detectors. According to this configuration, the inputs/outputs of an optical switch can be separately monitored.
Preferably, the supervisor monitors the abnormal operation of the first and second switches through the operation mode of the first and second switches controlled by the controller and the detection outputs from the first and second input detectors and first and second output detectors. With this function, it is possible to constantly monitor whether both first and second optical switches are appropriately operating or not.
Preferably, the optical cross-connector according to the invention further consists of an input detector to detect each of the plurality of input optical signals of the combiner, a first output detector to detect output light from each output port of the first optical switch, a second output detector to detect output light from each output port of the second optical switch, and a supervisor to monitor the detection outputs from the input detector and first and second output detectors. With this configuration, it is possible to reduce the means to detect inputs of an optical switch.
Preferably, the supervisor monitors the abnormal operation of the first and second switches through the operation mode of the first and second switches controlled by the controller and the detection outputs from the input detector and first and second output detectors. With this function, it is possible to constantly monitor whether both first and second optical switches are appropriately operating or not.
Preferably, the optical cross-connector according to the invention further consists of a first input detector to detect input light of each input port of the first optical distributor, a second input detector to detect input light of each input port of the second optical distributor, a first output detector to detect output light from each output port of the first optical distributor, a second output detector to detect output light from each output port of the second optical distributor, and a supervisor to monitor the detection outputs from the first and second input detectors and first and second output detectors. With this configuration, inputs/outputs of optical distributors can be separately monitored.
Preferably, the supervisor monitors the abnormal operation of the first and second distributors through the operation mode of the first and second distributors controlled by the controller and the detection outputs from the first and second input detectors and first and second output detectors. With this configuration, it is possible to constantly monitor whether both first and second optical distributors are appropriately operating or not.
Preferably, the optical cross-connector according to the invention further consists of an input detector to detect each of the plurality of input optical signals of the combiner, a first output detector to detect output light from each output port of the first optical distributor, a second output detector to detect output light from each output port of the second optical distributor, and a supervisor to monitor the detection outputs from the input detector and first and second output detectors. With this configuration, it is possible to reduce the means to detect inputs of optical distributors.
Preferably, the supervisor monitors the abnormal operation of the first and second distributors through the operation mode of the first and second distributors controlled by the controller and the detection outputs from the input detector and first and second output detectors. With this configuration, it is possible to constantly monitor whether both first and second optical distributors are appropriately operating or not.
Preferably, when the controller switches the first and second optical distributors from the first control state to the second control state, it sets the first optical distributor in the second connecting mode after or at the same time of setting the second optical distributor in the first connecting mode. With this operation, it is possible to reduce the time of signal break caused by the switching to the protection system into practically zero.